U.S. patent application number 13/349256 was filed with the patent office on 2012-07-19 for method and means for controlling the downshifting.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Gernot BECKER, Martin GENTILE, Wolfgang MOSER, Karlheinz SCHMITT.
Application Number | 20120184407 13/349256 |
Document ID | / |
Family ID | 46477645 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120184407 |
Kind Code |
A1 |
GENTILE; Martin ; et
al. |
July 19, 2012 |
METHOD AND MEANS FOR CONTROLLING THE DOWNSHIFTING
Abstract
A method is provided for controlling a downshifting of a
transmission of a motor vehicle in coasting mode from a staring
gear into a target gear. The method includes, but is not limited to
estimating an output torque exerted by the engine with starting
gear engaged, calculating a set point torque by means of the output
torque and the transmission ratios of starting and target gear, and
activating the engine with engaged target gear subject to the
presetting of the calculated set point torque.
Inventors: |
GENTILE; Martin;
(Koenigstaedten, DE) ; BECKER; Gernot; (Mainz,
DE) ; MOSER; Wolfgang; (Wiesbaden, DE) ;
SCHMITT; Karlheinz; (Hattersheim, DE) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
46477645 |
Appl. No.: |
13/349256 |
Filed: |
January 12, 2012 |
Current U.S.
Class: |
477/118 |
Current CPC
Class: |
Y02T 10/40 20130101;
F16H 2061/0496 20130101; B60W 30/192 20130101; Y10T 477/69
20150115; F16H 63/502 20130101; Y02T 10/76 20130101; Y02T 10/60
20130101; Y02T 10/48 20130101; B60W 10/11 20130101; B60W 10/06
20130101 |
Class at
Publication: |
477/118 |
International
Class: |
B60W 10/10 20120101
B60W010/10; B60W 10/06 20060101 B60W010/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2011 |
DE |
102011008597.1 |
Claims
1. A method for controlling a downshifting of a transmission of a
motor vehicle in a coasting mode from a starting gear into a target
gear, comprising: estimating an output torque exerted by an engine
with an engaged starting gear; calculating a set point torque with
a starting torque and a plurality of transmission ratios of the
starting gear and the target gear; and activating the engine with
an engaged target gear subject to the presetting of the set point
torque.
2. The method according to claim 1, wherein the estimating
comprises estimating the output torque without a supply of fuel to
the engine.
3. The method according claim 1, further comprising estimating the
starting torque with a predetermined function of a rotational speed
of the engine.
4. The method according claim 1, further comprising determining the
output torque with a change of a speed-based measurement
quantity.
5. The method according to claim 1, further comprising: comparing a
first deceleration of the motor vehicle after engaging the target
gear with a second deceleration before disengaging the starting
gear; adjusting the set point torque if a significant difference
exists between the first deceleration and the second
deceleration.
6. The method according to claim 1, further comprising gradually
reducing a fuel supply following the engaging of the target
gear.
7. The method according to claim 1, further comprising accelerating
the engine after disengaging the starting gear and before engaging
the target gear.
8. A computer readable medium embodying a computer program product,
said computer program product comprising: a control program for
controlling a downshifting of a transmission of a motor vehicle in
a coasting mode from a starting gear into a target gear, the
control program configured to: estimate an output torque exerted by
an engine with an engaged starting gear; calculate a set point
torque with a starting torque and a plurality of transmission
ratios of the starting gear and the target gear; and activate the
engine with an engaged target gear subject to the presetting of the
set point torque.
9. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
configured to estimate the output torque without a supply of fuel
to the engine.
10. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
further configured to estimate the starting torque with a
predetermined function of a rotational speed of the engine.
11. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
further configured to determine the output torque with a change of
a speed-based measurement quantity.
12. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
further configured to: compare a first deceleration of the motor
vehicle after engaging the target gear with a second deceleration
before disengaging the starting gear; and adjust the set point
torque if a significant difference exists between the first
deceleration and the second deceleration.
13. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
further configured to gradually reduce a fuel supply following the
engaging of the target gear.
14. The computer readable medium embodying the computer program
product according to claim 8, wherein the control program is
further configured to accelerate the engine after a disengagement
of the starting gear and before an engagement of the target gear.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to German Patent
Application No. 102011008597.1, filed Jan. 14, 2011, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The technical field relates to a method for controlling the
downshifting of a transmission of a motor vehicle, as well as a
computer and a computer program product for carrying out the
method.
BACKGROUND
[0003] Although when driving in coasting mode the engine of a motor
vehicle is connected to the chassis by way of the manual
transmission, it is not, however, supplied with fuel so that the
movement of the vehicle keeps the engine running and not the other
way around. When rolling on a level or rising road surface, this
leads to a continuous deceleration of the vehicle and, accordingly,
to a reduction of the rotational speed of the engine.
[0004] Conventional automatic gear changes are equipped to select
and engage in the transmission a gear of the transmission by means
of the engine rotational speed and/or the vehicle speed. In
general, limit values of the speed and/or of the rotational speed
are defined for each gear, the undershooting of which results in
that the next lower gear is automatically engaged. When a vehicle
rolls on a level road surface in coasting mode, these limit values
are successively undershot. Such downshifting in each case leads to
a rotational speed increase of the engine and to an increase of its
deceleration effect. An abrupt change of the deceleration is
perceived as impairment of the travelling comfort. Although it is
conceivable per se to bring about a gradual change of the
deceleration through slow closing of the clutch, but an
unnecessarily long sojourn of the clutch in a partly open state
leads to increased friction wear and is therefore undesirable.
[0005] At least one object is to create a method for controlling
the downshifting of a motor vehicle transmission that avoids an
impairment of the travelling comfort through abrupt deceleration
change. In addition, other objects, desirable features, and
characteristics will become apparent from the subsequent summary
and detailed description, and the appended claims, taken in
conjunction with the accompanying drawings and this background.
SUMMARY
[0006] A method is provided for controlling a downshifting of a
transmission of a motor vehicle in coasting mode from a starting
gear into a target gear with the steps of: a) estimating a starting
torque exerted by the engine with the starting gear engaged, b)
calculating a setpoint torque for the target gear by means of the
starting torque and the transmission ratio of starting gear and
target gear, and c) activating the engine with engaged target gear
subject to the presetting of the calculated setpoint torque.
[0007] The product of starting torque and starting rotational speed
is a dimension for the power absorbed by the engine before the
downshifting drawn from the kinetic energy of the vehicle, i.e.,
for the deceleration effect of the engine. In order for this power
and as a consequence the deceleration of the vehicle after the
downshifting to be the same as before, the product of torque and
transmission ratio after the downshifting has to remain the same.
This requirement results in the setpoint torque to be generated by
the engine after the downshifting.
[0008] Preferably, the method is employed when the vehicle rolls
out entirely without drive, for example, when approaching a red
traffic light. In this case, the estimation of the starting torque
in step a) takes place entirely without supply of fuel to the
engine. However, also conceivable is an application in cases where
the driver actuates the accelerator pedal of the vehicle but not
forcefully enough in order to maintain the speed of the
vehicle.
[0009] The estimation of the starting torque can take place based
on the rotational speed of the engine by means of a preset
function, which can be stored as table or as computation
instruction. Apart from the rotational speed, this function can
also depend on other influence factors measurable on the engine or
transmission, in particular on their temperature. It is also
conceivable to determine the starting torque by means of the time
change of a speed-based measurement quantity such as for example
the vehicle speed or the rotational speed of the engine or any
other rotating component of the drive train of the vehicle. Such a
change can be directly utilized for estimating the starting torque,
or it can serve for the continuous updating of the preset function
mentioned above.
[0010] Unforeseen environmental influences can be taken into
account in that the deceleration of the vehicle following the
engagement of the target gear is compared with the deceleration
before disengaging the starting gear and in the event of a
significant difference between the decelerations; the set point
torque is readjusted. Following the engaging of the target gear a
fuel supply required for generating the setpoint torque calculated
in step b) can be gradually reduced so that the deceleration of the
vehicle gradually reaches the value to be expected for a fewer
coasting mode in the target gear.
[0011] In order to avoid a shock that can be felt by the vehicle
occupants that would result if upon engaging of the target gear the
engine would be abruptly accelerated via the transmission, the
engine can be supplied with a metered amount of fuel even during
the shifting in order to accelerate said engine before the target
gear is engaged.
[0012] A computer, particularly an engine control unit for a motor
vehicle, which is equipped to carry out the method described above,
or a computer program product with program code means more
preferably stored on a data carrier, which enable a computer to
carry out the method described above, is also an embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will hereinafter be described in
conjunction with the following drawing figures, wherein like
numerals denote like elements, and:
[0014] FIG. 1 is a schematic representation of a drive train of a
motor vehicle subjected to the method according an embodiment;
[0015] FIG. 2 is a flow diagram of the method according to the
embodiment;
[0016] FIG. 3 is the time development of rotational speed and
engine torque when carrying out the method according to FIG. 2;
and
[0017] FIG. 4 is a flow diagram of additional steps of a further
development of the method of FIG. 2.
DETAILED DESCRIPTION
[0018] The following detailed description is merely exemplary in
nature and is not intended to limit application and uses.
Furthermore, there is no intention to be bound by any theory
presented in the preceding background or the following detailed
description.
[0019] FIG. 1 is a block diagram of a motor vehicle drive system
implementing the embodiment with a combustion engine 1, a stepped
transmission 2, a differential 3, and wheels 4 driven via the
differential 3. The stepped transmission 2 can be an automated
shift transmission that is connected to the combustion engine 1 via
a clutch 5, or an automatic transmission, wherein a torque
converter takes over the function of the clutch. In the following,
for the sake of simplicity, however, only the clutch 5 will be
discussed. However, it is to be understood that the functions of
said clutch, as soon as these are relevant to the present
invention, can also be carried out by the torque converter.
[0020] An electronic control unit 6 monitors and controls the fuel
supply of the combustion engine 1 corresponding to the actuation of
an accelerator pedal by the driver or corresponding to a presetting
by a driver assistance system (not shown). In addition, it controls
the gear engaged in the stepped transmission 2 by means of the
rotational speed sensed by a rotational speed sensor 7 on the
output shaft of the engine 1 and/or of the speed of the vehicle,
which can be obtained with the help of a speedometer sensor 8
sensing the rotational speed of a shaft of the drive train located
on the output side of the stepped transmission 2.
[0021] In order to control a gear change, the control unit 6 acts
on the clutch 5 and on the stepped transmission 2 via actuators 9,
10. The control unit 6 can be a microcomputer with a single
processor, which accomplishes both the control of the combustion
engine 1 as well as that of the clutch 5 and of the transmission 2;
however, it can also comprise two separate processors, of which a
first one controls the engine and the second one the gear selection
and makes available to the first processor information necessary
for the engine control concerning a currently engaged gear or a
gear soon to be engaged next. The second processor controlling the
transmission and the clutch can also be omitted in favor of a
conventional hydraulic automatic gear change, provided the
processor controlling the engine 1 is connected to the required
sensors in order to detect the respective gear currently engaged
and a gear to be engaged next if applicable by means of measured
rotational speeds and/or speeds all or pressures measured in the
automatic gear change. The control unit 6 is furthermore
connectable to sensors 11 for sensing the temperature of the engine
1 and of the transmission 2 as well as of other operating
parameters connected with losses of the engine 1 and of the
transmission 2.
[0022] FIG. 2 shows a flow diagram of an exemplary operating method
of the control unit 6. With the description, it is assumed that at
the start of the method a gear g is engaged in the transmission 2
and that this gear g is known to the control unit 6. Furthermore,
it is assumed for the sake of simplicity that the gear selection is
merely based on the vehicle speed v. It is to be understood however
that further criteria such as the rotational speed of the engine 1
can be taken into account instead of or in addition to the speed
v.
[0023] In step S1, the control unit 6 checks if a condition for the
downshifting, here the undershooting of a minimum speed v.sub.min,g
is satisfied for the current gear g. For as long as this is not the
case, the step S1 is regularly repeated. Once the downshift
criterion is satisfied, at the latest, the control unit 6 estimates
the torque M.sub.g acting on the output shaft of the engine 1. When
the vehicle is purely in coasting mode, i.e. when the accelerator
is not actuated and the engine 1 is consequently not supplied with
fuel, this torque M.sub.g is a function M(n,T) of the engine
rotational speed n and the temperature. This function M(n,T) is
always negative, i.e. the torque M.sub.g has a decelerating effect
on the vehicle. The amount of M slightly increases with the
rotational speed n and, because of the improved lubricity of the
engine oil with increasing temperature T, decreases with the
temperature T. Preferentially, the function M(n,T) is stored in a
memory of the control unit 6 in the form of a search table.
[0024] In step S3 the control unit 6 calculates a setpoint torque
of the engine M.sub.s,g-1, which the engine 1 upon downshifting in
the next lower gear g-1 would have to exert so that the
downshifting remains without effect on the deceleration of the
vehicle. This setpoint torque M.sub.s,g-1 is obtained by
multiplication of the current torque M.sub.g with a correction
factor derived from the transmission ratios i.sub.g, i.sub.g-1 of
the gears g, g-1:
M s , g - 1 = i g i g - 1 M g . ##EQU00001##
[0025] In order to avoid that an abrupt rotational speed increase
of the engine 1 driven by the vehicle movement following the
downshifting in the gear g-1 results in a shock that is noticeable
to the occupants it is practical during the downshifting to
increase the rotational speed of the engine from the rotational
speed n at the time of the shifting decision to the value
i.sub.g-1*n/i.sub.g. The kinetic energy of the rotating parts of
the engine required for this now is:
.DELTA. E kin = .pi. 2 2 I ( i g - 1 2 i g 2 - 1 ) n 2 ,
##EQU00002##
where I describes the moment of inertia of the rotating parts of
the engine 1. If .DELTA.t is the duration of the shifting operation
available for increasing the rotational speed, the mean torque to
be exerted by the engine in this time is obtained as:
M trans = 2 .pi. In .DELTA. t ( i g - 1 - i g i g - 1 + i g ) ( S 4
) . ##EQU00003##
[0026] As soon as in step S5 the starting gear g is disengaged, the
control unit 6 signals to the engine 1 the setpoint torque
M.sub.trans (S6), which said engine has to generate in order to
increase its rotational speed during the course of the shifting
operation to i.sub.g-1*n/i.sub.g. When in step S7 the gear g-1 is
engaged, the engine 1 therefore has reached the corresponding
suitable rotational speed, i.e. parts of the clutch 5 on the drive
side and output side rotate at the same speed. Following the
closing of the clutch 5, the engine 1 is activated in step S8 with
the setpoint torque M.sub.s,g-1 calculated in step S3. The
deceleration of the vehicle is therefore no different after
engaging the target gear g-1 than prior to the shifting, and the
shifting operation is therefore not perceptible to the vehicle
occupants.
[0027] Only after the shifting will the fuel supply to the engine 1
be gradually reduced from the value required for generating the
torque M.sub.s,g-1 back to zero in step S9, in order to let the
vehicle continue to roll in coasting mode. The duration of this
step S9 can be as long as required in order to avoid letting the
increase of the deceleration become perceptible to the vehicle
occupants.
[0028] FIG. 3 schematically shows the time curve of the rotational
speed and the torque of the engine 1 during a downshift operation.
A dash-dotted horizontal line in FIG. 3 describes the limit
rotational speed n.sub.min,g of the engine corresponding to the
limit speed v.sub.min,g in the gear g. In a time span before the
time t.sub.1 corresponding to the repeated execution of the step S1
the rotational speed n uniformly decreases until at the time
t.sub.1 the shifting threshold is reached. The torque of the engine
is constantly negative at M.sub.g. At the start of the shifting
operation, it assumes the positive value M.sub.trans, and the
rotational speed n uniformly rises until at the time t.sub.2 the
target gear g-1 is engaged. The setpoint torque M.sub.s,g-1
applicable from t.sub.2 is smaller than M.sub.trans and can,
deviating from the representation of FIG. 3, also be between zero
and M.sub.g.
[0029] In the representation of FIG. 3 a time interval [t2, t3]
exists between the steps S8 and S9, in which the control unit 6
maintains the setpoint torque Ms,g-1 unchanged and in which the
deceleration of the vehicle is the same as before the time t1 . The
duration of this time interval can also be zero, however. From the
time t3, the control unit 6 gradually reduces the fuel supply to
the engine 1. As is evident from the development of the rotational
speed in FIG. 3, the deceleration of the vehicle also increases
gradually until at the time t4 the fuel supply is again zero and
the deceleration again reaches a constant value. If it is not the
lowest gear of the transmission 2, the gear g-1 so reached in turn
can serve as starting gear for a repetition of the method.
[0030] The torque determined in step S2 by means of the search
table M(n,T) need not necessarily coincide exactly with that
actually exerted by the engine 1. Deviations can for example be due
to manufacturing tolerances between an engine used for creating the
search table and the engine 1 of the vehicle or due to ageing
manifestations of the engine 1. Such inaccuracies could be avoided
in principle by determining the engine torque M.sub.g in real time
in each case. Such a real time determination, which can be based on
the time change of the vehicle speed or a quantity which has a
fixed known relationship with said vehicle speed such as for
example the rotational speed, however has the problem that it is
influenced by environmental influences such as for example an
incline of the road surface that is different from zero or the
rolling resistance of the vehicle that is dependent on the quality
of the road surface. Since these influences tend to balance out on
average, such a real time determination can be practically employed
for a running updating of the search table.
[0031] Such an updating can be carried out for example in that the
steps shown in FIG. 4 are inserted in the method of FIG. 2 at any
point between step S1 and S5. In step S11, an alternative value
M.sub.g' of the engine torque is initially calculated as a function
of vehicle mass and vehicle deceleration. The vehicle deceleration
can be directly measured for example by an inertia sensor or it can
be numerically calculated as time derivative from speed values or
from values of a quantity, such as for example the engine
rotational speed, that has an unambiguous relationship with the
vehicle speed. In step S12, it is decided if this alternative value
and the value of the engine torque calculated after step S2 differ
significantly by more than a limit value .delta.. If there is such
a significant difference, the search table M(n,T) is corrected in
step S13. The correction in each case relates only to that value of
the search table that corresponds to the current parameter values
of n and T and has been utilized for determining the engine torque
in step S2. In each case, this value is increased or reduced by a
fixed small increment .epsilon., depending on which of both is
necessary in order to reduce the difference between the two torque
values M(n,T) and M.sub.g'. The smaller .epsilon., the greater the
number of measurements that is required in order to make the search
table agree with the true value of the engine torque, but the more
completely is the influence of a road surface inclination randomly
varying from one measurement to the other averaged.
[0032] While at least one exemplary embodiment has been presented
in the foregoing detailed description, it should be appreciated
that a vast number of variations exist. It should also be
appreciated that the exemplary embodiment or exemplary embodiments
are only examples, and are not intended to limit the scope,
applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment, it being understood that various changes may
be made in the function and arrangement of elements described in an
exemplary embodiment without departing from the scope of the
invention as set forth in the appended claims and their legal
equivalents.
* * * * *